Some types of lighting arrangements require a transformer to be used to obtain a certain voltage level. For example, halogen lamps require a transformer to convert the mains voltage to a lower level, usually 12 V. Halogen lamps typically consume 20 W-50 W of power. Generally, the transformer used to drive such a load is a switched-mode power supply that switches at a much higher frequency than the mains frequency. Usually, an electronic transformer operates according to a self-oscillating principle. However, this type of transformer does not work well with the newer LED-based lamps, since LED light sources have a much higher lumen per Watt ratio and consume significantly less power than their halogen counterparts. A self-oscillating electronic transformer requires a minimum load current (i.e. the current through the light source) in order to maintain the oscillation. However, since an LED draws significantly less current than a halogen lamp, when it is driven using an electronic transformer of the type described above, the self-oscillation of the electronic transformer can be interrupted. Particularly when a dimmer is used in conjunction with such an LED lamp, the interruptions in the electronic transformer's self-oscillations result in unstable dimmer operation. This can result in noticeable flicker in the light output of the LED.
This incompatibility is a problem when it is desired to replace a halogen light source of an existing lighting arrangement by an equivalent LED light source. Here, “equivalent” is to be understood in the context of lamp type, for example the MR16 lamp type defines the lamp socket and the lumen output. Such retro-fitting is desirable from an environmental point of view, since LED light sources generally have a significantly longer lifetime than halogen light sources, and consume significantly less power. Generally, it is only possible to access the light source of such a lighting arrangement that already includes a dimmer and transformer, but since the electronic transformer (and dimmer) cannot be accessed for modification, even by a skilled technician, an LED light source that uses relatively low power usually cannot be used to replace a “normal power” halogen light source.
Therefore, it is an object of the invention to provide an improved lighting arrangement that avoids the problems outlined above.